Genome-wide associated studies have demonstrated that in chronic inflammatory diseases - such as chronic obstructive pulmonary disease (COPD) and asthma - IL-33 expression is highly upregulated; however, its function in the pathology of these diseases is undetermined. A possible explanation is that IL-33 is continuously released by failures in acute inflammation resolution, resulting in excess damage and inhibiting healing. However, our current understanding of IL-33 function in inflammation resolution and healing changes are insufficient to explain the inflammatory phenotype seen in chronic lung disease. Furthermore, the early innate inflammatory response mediated by IL-33 are not well characterised, and understanding this may be able to provide insights to the phenotypes seen in chronic inflammation. This study aimed to understand how IL-33 modulates the innate immune response during inflammation and infection and how this may inform phenotypes seen in chronic inflammatory disease. For in vivo murine studies modelling inflammation, BALB/c wild type (WT) and ST2 knock-out (KO) mice were treated with Alternaria alternata for 30 minutes, 1- and 5 – hours. Precision-cut lung slices (PCLS) were generated for imaging and cytokine analysis. For imaging, PCLS were fluorescently stained to tag macrophages, neutrophils, and eosinophils and imaged using epifluorescent wide-field microscopy. Immune cells, morphological characteristics and neutrophil clusters were quantified. For in vivo murine studies modelling infection, BALB/c WT and ST2 KO mice were infected with Streptococcus pneumoniae and Influenza A virus (IAV) for 24 hours and 4 days, respectively. Immune cells, cytokine concentrations, morphological characteristics, neutrophil clusters, pathogen burden and clinical symptoms were quantified. For in vitro human infection studies, human bronchial epithelial cells (HBEC) were differentiated into air-liquid interface (ALI) cultures from healthy and COPD samples that were infected with IAV for 48 and 96 hours. Pot infection, mucin proteins, cytokine and RNA expression were analysed. From the in vivo inflammation studies, no differences in immune cell numbers were quantified at 30 minutes, 1 hour, and 5 hours from baseline. However, there was a significant increase in neutrophil clusters 5 hours post A. alternaria treatment. IL-10 concentration also increased in ST2 KO mice after A. alternaria treatment. Post S. pneumoniae and IAV infection, no differences between mouse genotypes were seen in immune cell infiltration, neutrophil cluster formation, pathogen burden, clinical symptoms, and cytotoxicity. In ST2 KO mice, Interferon gamma-induced protein 10 (IP-10) and tumour necrosis factor (TNF-α) levels increased post-S. pneumoniae infection and monocyte chemoattractant protein-1 (MCP-1) levels increased post-IAV infection. In HBEC ALI cultures, neutralisation of IL-33 decreased CST1 and SPDEF expression in COPD HBEC ALI cultures. Post-IAV infection, CXCL10 expression significantly increased in healthy HBEC ALI cultures. These novel findings demonstrate a previously undefined role for how IL-33 may drive disease and inform phenotypes seen in chronic disease. These data highlight the importance of IL-33 blockade for therapeutic intervention for such diseases, but further work is required to better understand these data.
